The invention relates generally to the field of magnetic bubble technology (MBT) and, more particularly, to means for propagating or transmitting magnetic bubbles.
Briefly, MBT involves the creation and propagation of magnetic bubbles in specially prepared magnetic materials. The word "bubble" used throughout this text is intended to encompass any single-walled magnetic domain, defined as a domain having an outer boundary which cloes on itself. The application of a static, uniform magnetic bias field orthogonal to a sheet of magnetic material having suitable uniaxial anisotropy causes the normally random, serpentine pattern of magnetic domains to shrink into short cylindrical configurations or bubbles whose common polarity is opposite that of the bias field. The bubbles repel each other and can be moved or propagated by a magnetic field in the plane of the sheet.
Many schemes now exist for propagating bubbles along predetermined channels. One system includes permalloy circuit elements shaped like military service stripes or "chevrons" spaced end-to-end in a thin layer over the sheet of magnetic material. The drive field is caused to rotate continuously in the plane of the sheet, for example, by using a Helmholtz coil arrangement, making each chevron act as a small magnet with changing poles. As the drive field rotates, a bubble under one of the chevrons is moved along the chevron channel from point-to-point in accordance with its magnetic attraction to the nearest attracting temporary pole among the circuit elements. This system is among those referred to as "field-accessed," as distinguished from other systems employing sequentially pulsed loops of electrical conductors disposed in series over the magnetic sheet.
MBT can be used in data processing because magnetic bubbles can be propagated through channels at a precisely determined rate so that uniform data streams of bubbles are possible in which the presence or absence of a bubble indicates a binary "1" or "0."
Because of the difficulties in implementing continuous patterns of conductor overlays, field-accessed circuits have in general been considered potentially superior to conductor-accessed circuits. Uniformly rotating magnetic drive fields have been used in most field-accessed circuit arrangements. Some field-accessed circuits using a nonrotating magnetic drive field are shown in U.S. Pat. No. 3,543,252 to Perneski. Variations on the familiar T-bar circuit are described, driven by various permutations of orthogonal fields. U.S. Pat. No. 3,518,643 to Perneski illustrates a continuous zigzag pattern overlay arrangement driven by an in-plane, reorienting drive field repeatedly switched over an arc of 90.degree..